Heating the interior spaces of buildings and producing hot water account for a major portion of the energy use in a typical home. Traditional methods for solar space heating maximize interception of sunlight in winter, yet minimize it in summer by placing awnings over windows or landscaping with deciduous trees. Also, sophisticated, low-temperature solar thermal systems are available to collect sunlight for space and water heating.

For example, glass-enclosed flat-plate solar collectors on rooftops have black plates that absorb sunlight and transfer the thermal energy to fluids (water or a less-corrosive liquid) passing through flow tubes lying flat against the surface of the plates.

Glazed flat-plate solar collector for heating buildings.

A black absorber plate, oriented toward the sun, warms the fluid passing through the flow tubes.

More efficient, but more expensive, systems use receiver tubes similar to those in parabolic trough solar systems. The fluid heated in flow or receiver tubes goes into the building to warm the interior, generate hot water, or both.

Solar residential heating is becoming more commonplace. Israel—a country blessed with ample sunlight but little petroleum—leads the world in solar heating systems per capita, and solar water heating accounts for 3.4% of the country’s total energy consumption. [1] In terms of sheer number of installations, however, China dominates: The country accounts for about 75% of the global capacity added in 2006 and for nearly 65% of the world total. Half of the households in some Chinese cities use solar water heaters. [2]